Step-by-step electric motor



April 27, 1954 B. c. FLEMING-WILLIAMS ET AL 2,677,090

STEP-BY-STEP ELECTRIC MOTOR Filed Sept. 11, 1950 I5 Sheets-Sheet l INVENTOR .F/cmin -Wi/l/ams 5213?"? R. We W 4 April 1954 B. c. FLEMING-WILLIAMS ET AL 2,677,090

STEP-BY-STEP ELECTRIC MOTOR 5 Sheets-Sheet 2 Filed Sept. 11, 1950 W ww m 2 m W l \l fi w, m 2m w E A m Z 3 4 \g 7// w mg k Kw April 27, 1954 B. c. FLEMING-WILLIAMS ET AL 2,677,090

STEP-BY-STEP ELECTRIC MOTOR Filegl Sept. 11, 1950 3 Sheets-$heet 5 .ZNVENTORS Brian C. Fleming- Williams filamem R.W0odwam' UNITED STATES STEP-BY-STEP ELECTRIC MOTOR Brian Clifford Fleming-Williams and Clement Ralph W'oodward, London, England, assignors to A. C. Cossor Limited, London, England, a company of Great Britain Appiication September 11, 1950, Serial No. 184,172

Claims priority, application Great Britain September 13, 1949 1 Claim. (01. 318-443) 1 2 The present invention relates to stepby-step gised by pulsating or alternating current to cause electric motors, that is to say motors of the type the states of magnetisation of the said adjacent in which the rotor is adapted to execute steppoles to be varied diiferentially, the rotor memby-step rotation on the application of pulsating ber rotates in step-by step fashion, each step or alternating current to the motor. being effected by a reversal of the relative mag- Such motors may be employed for a variety netic states of the said adjacent poles. The

stem OFFICE of purposes such as, for example, for counting torque-producing poles on the two members are the number of pulses or cycles of current occurthose between which, in operation, forces exist ring in a circuit or for the remote operation of to. produce rotation of the rotor member. One a switch coupled to the motor. 3 or more other poles may be provided for the pur- A known motor of this type comprises a pose of completing the magnetic circuit from toothed wheel whose teeth are engaged in turn the rotor member back to the stator member or by a claw which is actuated by an electro-magvice versa. The said face of each torque-producnet. Each pulse applied to the electro-magnet ing pole on each member is that face through causes the claw to rotate the wheel through a 5 which the majority of the magnetic flux passes predetermined angle, the claw being released at when facing a D 011 the other mmbel the end of the pulse to engage with a further Further according to the invention, a motor of tooth. the type specified comprises two members,

An object of the present invention is to pronamely a ro r n a s r, of rm-m neti vide an improved motor of the type specified in material, o e av at least two q -p which the only moving part need be a rotor, stepi s po s d the other having at least three by-step rotation of the rotor being produced torque-pr i 130165, e numbers of q entirely electrically. producing poles on the two members being un- According to the present invention, a motor equal, t e rotor m b being u t for t of the type specified comprises two members, 5 tion relatively to the stator member in such a namely a rotor and a stator, of ferro-magnetic manner that the faces of the torque-producing material, one having at least two torque-propol s 0 th rotor m m can be u t in 1 ducing poles and the other having at least three cession before the face of each of the torquetorque-producing poles, the rotor member being producing poles on the stator member, the promounted for rotation relatively to the stator jection of the face of each torque-producing pole member in such a manner that the faces of the of one of the members on to the surface swept torque-producing poles on the rotor member out by the outer extremities of the torque-procan be brought in succession before the face of ducing poles on the rotor member, having a each of the torque-producing poles on that length, measured in the direction of relative stator member, the projection of the face of each ,W movement of such pole with respect to a facing torque-producing pole of one of the members pole on the other. member, which is greater than on to the surface swept out by the outer exthat of the projection of the face of each of the tremities of the torque-producing poles on the torque-producing poles of the other member on rotor member, having a length, measured in to the said surface, the major part of each pole the direction of relative movement of such pole 4G face of the said larger dimension lying in a surwith respect to a facing pole on the other memface whose distance from the surface swept out her, which is greater than that of the projection by the outer extremities of the torque-producing of the face of each of the torque-producing poles poles of the rotor member decreases, proceeding of the other member on to the said surface, windin the direction of rotation of the rotor member, ings being provided whereby each of the torquewhen this face is of a torque-producing pole on producing poles on one of the members can have the stator member, or roceeding in the opposite its state of magnetisation varied to either of direction when this face is of a torque producing two conditions, and whereby adjacent torquepole on the rotor member, whereby each face of producing poles on the last-named member can the said larger dimension has a region nearest have their states of magnetisation varied differ- 59 the last-named surface, the disposition of the entially to the two conditions, and the numbers torque-producing poles on the two members being and dispositions of the torque-producing poles such that when a pole face of the smaller dimenon the two members, and the shapes of the pole sion is facing the said region on a pole face of faces of the said larger dimension being such the said larger dimension, the said region on anthat, in operation, when the windings are enerother of the pole faces of the said larger dimension is not facing any pole face of the said smaller dimension, and that when the last-named pole face of the said larger dimension is of a torqueproducing pole on the stator member the torqueproducing pole nearest thereto on the rotor member lies in the opposite direction to the direction of rotation of the rotor member, or where the last-named pole face of the said larger dimension is of a torque-producing pole on the rotor member the torque-producing pole nearest thereto on the stator member lies in the direction of rotation of the rotor member, and windings being provided whereby each of the torque-producing poles on one of the members can have its state of magnetisation varied to either of two conditions and whereby adjacent torque-producing poles on the last-named member can have their states of magnetisation varied differentially.

The invention will now be described, by Way of example with reference to the accompanying drawings.

Figure 1 is a schematic drawing of one embodiment of the invention showing a rotor having ten torque-producing poles and a stator having four torque-producing poles.

Figure 2 shows the rotor of Figure 1 rotated through 18,

Figures 3 and 4 show a second embodiment of the invention in which the rotor has two torqueproducing poles and the stator has ten torqueproducing poles,

Figure 5 shows a third embodiment of the invention in which the rotor has three torqueproducing poles and the stator has two torqueproducing poles,

Figure 6 is a side view on a reduced scale showing part of the arrangement of Figure 5, and

Figure '7 shows a further embodiment of the invention in which the rotor is polarised.

The step-by-step motor shown in Figures 1 and 2 comprises a stator ii] having four poles ll, l2, l3 and I l, constituted by laminations held together by bolts (not shown) passed through eight apertures 15. A laminated rotor it has ten equally-spaced poles ii, and is mounted for rotation in the gaps between opposite poles on the stator. The stator poles H and i3 carry single windings l8 and Iii respectively, and the stator poles i2 and I4 each carry two windings 2Q, 21 and "22, 23 respectively. The windings l8, l9, 2|, 23 are connected in series or in parallel to two terminals 2%, 25 and windings 2i and 22 are connected in series or in parallel to two terminals 26 and 21, the parallel connections being shown.

In operation direct current is applied to the terminals 26 and 21 and pulses are applied to the terminals 2d and 25, the pulses being generated in any suitable manner. It is arranged that the rotor rotates in the direction indicated by the arrow 28 and is shown in a position occupied when the amplitude of the applied pulses is zero, that is to say when the magnetisation produced by the windings l8, l9, 2| and '23 is zero. The windings and 22 are continuously energised, however, causing magnetisation of the stator poles i2 and Hi, and two diametrically opposite rotor poles are attracted to the stator poles l2 and i4 and held in this position as shown.

The face of each stator pole is arranged to lie in a plane at right angles to the stator pole axis, the axes of the stator poles l2 and M are arranged to be parallel to, but offset respectively above and below, the horizontal plane passing through the rotor axis, and the axes of the stator poles H and 53 are arranged to be parallel to, but offset to the left and right respectively of, the vertical plane passing through and parallel with the rotor axis. The surface swept out by the faces of the rotor poles is indicated by a broken line 29 and it will be seen that because of the disposition of the stator poles the faces thereof approach this surface in the direction of rotation of the rotor. The position of the rotor giving the minimum gap between the rotor poles and the stator poles l2 and H5 is, as shown, that in which the rotor poles opposite the stator poles l2 and it are near the lower and upper edges of these stator poles respectively. The rotor therefore takes up that position. It will be appreciated that in order to obtain this position of the rotor the dimension of the projection of the face of each rotor pole on to the surface 29, measured in the direction of a relative movement between this pole and a facing stator pole must be substantially smaller than the dimension in the said. direction of the projection of each stator pole face on to the surface 23').

When a pulse is applied to the terminals 24 and 25, the stator poles H and I3 become magnetised and I2 and H become demagnetised, it being arranged that the magnetisation resulting from the application of the pulse to the windings El and 23 is substantially equal and opposite to that produced by the direct current flowing in the windings '29 and 22. It will be seen, therefore, that the pairs of poles l2, l4 and H, i3 have one state of magnetisation in which they are magnetised and another state in which they are demagnetised and that the two pairs of poles have their states of magnetisation varied differentially, that is to say one pair being magnetised when the other is demagnetised and vice versa.

It will be seen from the drawing that the distance between the stator pole H and the rotor pole immediately to the left thereof, is smaller than the distance between this rotor pole and any other stator pole. Furthermore the distance between the stator pole H and the rotor pole immediately to the right thereof is larger than the distance between the stator pole H and the rotor pole immediately to the left of the stator pole i 1. Similarly the distance between the stator pole l3 and the rotor pole immediately to the right thereof is shorter than the distance between this rotor pole and any other stator pole. The distance between the stator pole l3 and the rotor pole immediately to the left thereof is larger than the distance between the stator pole i3 and the rotor pole immediately to the right thereof. When, therefore, the pulse is applied to the terminals 24 and 25 rotation of the rotor takes place in the direction of the arrow 28 through approximately 18, and takes up the position shown in Figure 2.

On the cessation of the pulse the stator poles H and it become demagnetised and the stator poles l2 and Hi become magnetised. The rotor then makes a further rotation of 18 in the direction of the arrow 28 to bring the rotor into a position advanced on that shown in Figure l by the rotor pole pitch.

For each applied pulse the rotor therefore makes two rotational steps through angles of 18 each, and hence ten pulses are necessary to produce one complete revolution of the rotor.

Alternating current may be applied to the terminals 2G and 25 instead of pulsating current.

In this case it is necessary to make the peak magnetisation of the poles l2 and Is resulting from the alternating current substantially equal to that produced by the direct current applied to the terminals 23 and 2?.

Although the embodiment described has ten rotor poles and two pairs of stator poles it will be understood that other arrangements of poles may be used. For example in the arrangement of Figure 1 it will be appreciated that two magnetic circuits are used, one including the stator poles i2 and Id and the rotor, the other including the stator poles El and I2 and the rotor. It will be appreciated that, in operation, torque-producing forces exist between each rotor pole and stator pole in turn. The stator poles I3 and it, or ii and [2, could be dispensed with provided a suitable flux path is provided, say through the rotor spindle. On the other hand, by increasing the number of stator poles the number of magnetic circuits may be increased.

Figure 3 shows an arrangement in which the rotor 16 has two torque-producing poles and the stator iii has ten equally-spaced torque-producing poles, and in which the operating windings are on the rotor poles. The dimension, of the projection of the face of each rotor pole on to the surface 29 measured in the direction of relative movement between this pole and a facing stator pole is made substantially larger than the dimension, in the said direction of the projection of the face of each of the stator poles on to the surface 29 as shown. The pole face of each rotor pole lies in a surface which approaches the surface 29 proceeding in the opposite direction to that of rotation of the rotor. With the rotor in the position shown in the drawing the region of the face of the pole 3D, nearest the surface 29, faces the stator pole 3 I, and the region of the face of the other rotor pole 32 nearest the surface 29 does not face any stator pole. It will be seen from the drawing that the stator pole nearest the rotor pole 32 is the stator pole 33 which lies in the direction of rotation from the rotor pole 32. The windings i8 and 2| on the rotor poles 3!! and 32 respectively are connected in series between two slip rings 34 and 35 whose brushes 36 and 37 are connected to the terminals 24 and 25 respectively. The winding 20 on the rotor pole 32 is connected between two slip rings 38 and 33 whose brushes 4!] and 4| are connected to the terminals 26 and 21 respectively. Direct voltage is applied to the terminals 26 and 27 and pulsating, 0r alternating, voltage is applied to the terminals 25 and 25 as in the arrangement of Figure 1.

Referring now to Figure 4 this is a, view in cross-section taken at 4-4 in Figure 3, and shows the return flux path between the rotor and stator of Figure 3. The stator has two further poles 42 and 43 and the rotor spindle passes between the faces of these pole pieces. It will be appreciated that the poles 42 and 43 and the spindle 45 do not have torque-producing forces between them to cause rotation of the rotor.

Referring again to Figure 3 this shows the rotor in a position when a pulse is already applied to the terminals 24 and 25 causing magnetisation of the rotor pole 30 and demagnetisation of the rotor pole 32. When the pulse is removed from the terminals 24 and 25 the rotor pole 30 becomes demagnetised and the rotor pole 32 becomes magnetised. The stator pole nearest to the rotor pole 32 is the stator pole 33 and hence the rotor rotates to a position in which the region of the face of the pope 32 nearest the surface 29 faces the stator pole 33. On the application of a further pulse to the terminals 24 and the rotor rotates to a position in which the region of the face of the pole 3i} nearest the surface 2s faces the stator pole t5. It will be seen, therefore, that each pulse applied to the terminals 24 and 25 cause the rotor to execute two rotational steps each of about 18 and hence ten pulses are required to make the rotor execute one complete revolution.

Figure 5 shows an embodiment of the invention in which the rotor [6 has three equallyspaced poles 65, ll and 48 and the stator has two poles 49 and 53 spaced as shown. The projection of the face of each of the two stator poles on to the surface 29 has a dimension, in the direction of relative movement between this pole and a facing rotor pole which is substantially larger than the dimension, in the said direction of the projection of the face of each of the r0- tor poles on to the surface 29. The stator poles 49 and 39 are provided with windings l8 and 2| respectively which are connected in parallel to the two terminals 2 and 25.

When the rotor is in the position shown no pulse is being applied to the terminals as and 25. As direct voltage is applied to the terminals 26 and 2! the stator pole 5B is magnetised and the rotor pole 4? is held in the position shown. The rotor pole nearest to the stator pole as is the rotor pole 23. When, therefore, a pulse is applied to the terminals 24 and 25 to demagnetise the stator pole 50 and to magnetise the stator pole 49 the rotor rotates through 60 in the direction of the arrow 28 to the position in which the rotor pole 33 faces the region of the face of the pole 43 nearest the surface 29. When the pulse is removed the rotor rotates a further 60 in the direction of the arrow 28 to a position in which the rotor pole 46 occupies the position occupied by the pole er in the drawing. It will be seen, therefore, that it is necessary to apply three pulses to produce one complete revolution of the rotor.

In the arrangement of Figure 5 each stator pole has a separate magnetic circuit and Figure J6 shows the return path for the flux in the stator pole 49, the pole to being omitted. It will be seen that this path for the stator pole 49 is through an arm 5! and a pole 52 back to the rotor I6.

Figure 7 shows an arrangement in which the numbers and dispositions of the poles on the rotor and stator are the same as in Figure 5. The rotor is, however, polarised in this example in such a manner that each rotor pole is a north magnetic pole. A winding 53 on the stator pole 49 is connected in parallel with a winding 53 on the stator pole 53 to the terminals 26 and 21 to which direct voltage is applied. A winding 55 on the stator pole 43 is connected in parallel with a winding 56 on the stator pole 50 to the terminals 2:: and 25 to which pulses are applied.

The windings 53 and 5s and the polarity of the direct voltage applied to the terminals 26 and 21 are made such that in the absence of a pulse at the terminals 24 and 25 the stator pole 50 is a south magnetic pole and the stator pole 49 is a north magnetic pole. The rotor then takes up a position, as shown, with one of its poles facing the region, on the stator pole 50, nearest the surface 29.

The windings 55 and 56 and the polarity and.

magnitude of the pulses applied to the terminals 24 and 25 are arranged to be such that each applied pulse causes the stator pole 49 to become a south magnetic pole and the stator pole 5|] to become a north magnetic pole. In this way the magnetic states of the stator poles are varied diirerentially to two conditions. In one condition the stator poles 49 and 50 are north and south magnetic poles respectively and in the other condition the stator poles 49 and 50 are south and north magnetic poles, respectively.

When the stator poles 49 and 50 are made south and north magnetic poles respectively, on the application of a pulse to the terminals 2 4 and 25, the rotor pole 56 is attracted towards the stator pole 49 and the rotor pole 41 is repelled away from the stator pole 50. tates, therefore, through 60 in the direction of the arrow 28 and takes up a position in which the rotor pole 48 faces the region on the stator pole 49 nearest the surface 29. When the pulse ceases the rotor pole 46 being nearer to the stator pole .iil'than the rotor pole 41 is attracted towards the stator pole 50 and the rotor rotates through a further 60. As in the arrangement of Figure 5, therefore, three pulses are required to produce one complete revolution of the rotor.

In the arrangements hereinbefore described the speed of operation may be made as high as, say,

1 /2 complete revolutions per second by suitably designing the motor, and for operation at these speeds it may be found necessary to apply a brake to the rotor shaft. The brake may be arranged to apply a constant braking force for example by means of friction. On the other hand the brake may be arranged to apply a braking force which is dependent upon the speed The rotor 10- of rotational? the rotor, the braking force increasing with increase in speed and decreasing with decrease in speed. The brake may also be in the form of an oscillation damper such, for example, as described at page 332 in volume 21 (entitled Electronic Instruments) of the Massachusetts Institute of Technology Radiation Laboratory Series, published by the McGraw- Hill Book Company.

We claim:

A step-by-step electric motor comprising a stator having a plurality of torque-producing poles, a rotor having a plurality of torque-producing poles that are constantly polarized with like polarity, first and second windings on one of said stator poles, first and second windings on another of said stator poles, said two first windings being oppositely poled, and said two second windings being oppositely poled, means connecting said two first windings to a source of direct current to provide for normally biasing said stator poles with opposite polarity, and means connecting said two second windings to a source of spaced current pulses of magnitude suflicient to reverse the polarity of said biased stator poles during each pulse of current.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,502,840 Beard July 29, 1924 1,787,620 Favarger Jan. 6, 1931 1,990,665 Hyburg Feb. 12, 1935 2,499,316 Johnson Feb. 28, 1950 FOREIGN PATENTS Number Country Date 28,539 Great Britain of 1902 

